The proposed project is an investigation of genetic restriction at the level of transcription during animal development. The system to be studied is postgastrula development in the brine shrimp, Artemia salina. The objective will be to try to correlate changes in the transcription apparatus with the decline in RNA synthesis that occurs during this stage of development. Soluble RNA polymerase will be purified by combinations of column chromatography, sucrose gradient centrifugation, and isoelectric focusing. The subunit structure of purified polymerases will be examined by SDS-gel electrophoresis and by gel electrofocusing. Distribution of multiple forms of RNA polymerase will be determined by column chromatography. Nuclei will be isolated from developing embryos and used to study RNA synthesis in vitro. Synthesis of pre-ribosomal RNA will be used as a criterion of fidelity of transcription. Experiments will be conducted to determine whether the decline in RNA synthesis observed in intact animals is reproduced in the isolated nuclei.